Machine guns are typically switched between semiautomatic and full automatic modes of operation by operating a selector switch. It is often difficult for the operator to remember the proper direction of movement to switch between the full and semiautomatic modes, especially in the heat of battle, or if the gun is climbing out of control during full automatic operation. Reliability of operation is, of course, of great importance. Machine gun mechanisms often include a sear that is repeatedly hit during full automatic operation, and if that sear breaks, the gun cannot operate at all. A machine gun which could be switched between full and semiautomatic operation with a minimum possibility of error during a variety of stressful conditions, and which operated with high reliability, would be of considerable value.